Exporting 16x9 (anamorphic 720x480 DV) video for computer and internet playback :

The largest size is:

854x480

So from there you can do the math easily.

w: 854 x 9/16
h: 480 x 9/16

A few quick suggestions for DV:

720x405

640x360

480x270

428x240

360x202

280x157
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Other Formats:

(upscaling DV- may not always look good)

1920x1080 (1080i)

1280x720 (720p)

960x540